“…21n neoclassical models a change of technique is always obtainable with a continuous variation (or a variation that in the limit becomes continuous when there are infinitely many techniques) in any one coefficient at a time: this hypothesis can be found either in the earlier versions of marginal theory, where technology was represented by continuous, differentiable, concave production functions (see Wicksteed, 1894;Schneider, 1934), or in the modern formulations of general equilibrium models, where technology is described in terms of closed, bounded and convex "production sets". Recently aggregate production functions have enjoyed great favour in basic models of modern neoclassical macroeconomics (see Blanchard and Fisher, 1989, Chapters 2, 3 and 7), notwithstanding that the logical inconsistency of this tool has been demonstrated (see Garegnani, 1970).…”